The drilling of oil and gas wells in deep water has resulted in reaching the economic limits of bottom supported structures. Such bottom supported structures have reached their economic feasibility limit at depths between 500 feet to 1500 feet. In such range and deeper drilling and production are handled from floating structures. The movements of such floating structures creates serious problems of excess bending of production strings. To avoid this problem marine risers have been used to surround the production tubing. In such production systems, the floating structure cannot support the marine riser at various points along its entire length as could be done with a bottom-supported structure. Also, such marine riser systems have required subsea wellhead equipment and a disconnection of the riser and production strings with the occurrence of storm conditions.
The W. A. Hunsucker U.S. Pat. No. 3,454,116 provides external trusses and outwardly spaced tension members in an attempt to stiffen a riser pipe.
The K. A. Lehman U.S. Pat. No. 3,528,497 discloses a structure for supporting and positioning the upper end of a marine drilling string.
The K. A. Blenkarn et al U.S. Pat. No. 3,559,410 discloses supports for tension mooring members at the top and bottom to relieve stresses therein.
The K. A. Blenkarn U.S. Pat. No. 3,559,411 discloses a cable and pulley system coacting with mooring pipes to distribute the heave forces to the pipe.
The G. E. Mott et al U.S. Pat. No. 3,817,325 discloses a submarine conduit which is laterally reinforced by tension lines extending between vertically spaced arms extending outward from the conduit.
An article entitled "A 4,000-Foot Riser" by L. R. Heuze et al in the April 1976 edition of Journal of Petroleum Technology discusses the problems of production risers in deep water. It suggests a second support about 50 feet under the spider to reduce bending moments at the top of the riser.